The invention relates to an automated or semi-automated torque-transmitting system such as, e.g., the transmission of a vehicle. The torque-transmitting systems discussed here have a main drive clutch that couples the torque-transmitting system to a prime mover, a clutch-actuating means for controlling the state of engagement of the clutch, a transmission with a plurality of transmission ratios, a shifting mechanism for setting an operating ratio of the transmission, and a driver-operable mode-selector lever allowing a driver to select between a neutral mode or a drive mode of the. transmission.
In torque-transmitting systems of this type, when starting from a stand-still, the clutch is in the disengaged condition and a start-up gear is selected automatically. Then, the clutch is engaged as the accelerator pedal is actuated. A torque-transmitting system of this type is disclosed in UK Patent No. 2302377, whose content is hereby expressly included by reference in the disclosure of the present application.
Typically in torque-transmitting systems of this type, upon starting the engine the torque-transmitting system is activated and the clutch is automatically disengaged. Moving the mode-selector lever, which may be a selector or shift lever, from a neutral mode N to a drive mode, e.g., D (forward drive) or R (reverse) will cause a start-up gear to be automatically selected.
The disengagement of the clutch when the transmission is being activated has the disadvantage that the transmission input shaft is not set in motion. Consequently, no rotation of meshed gears is taking place to warm up the transmission oil.
Therefore, if the engine is left running to warm up after a cold start, the engine coolant and engine oil will be brought up to temperature, but the transmission oil, and thus the transmission itself, will not be warmed up.
It is therefore the object of the present invention to further develop a torque-transmitting system of the kind described above, so that the transmission, too, will be warmed up when the engine is left running after a cold start.
According to one aspect of the present invention, the foregoing objective is met by a torque-transmitting system for vehicles that belongs to the kind described above and is further equipped with electronic control means to control the clutch-actuating means and the shifting mechanism, where the electronic control means will cause the clutch-actuating means to disengage the clutch when the engine is started and will also cause the clutch-actuating means to re-engage the clutch in the case where the transmission has been left in neutral mode for a preprogrammed time period while the vehicle is standing still.
Re-engaging the clutch in this manner will cause the transmission input shaft to be driven so that the rotation of meshed gears will warm up the transmission oil.
According to a preferred embodiment of the present invention, the preprogrammed time period is of the order of 5 seconds. Preferably, re-engagement of the clutch in this manner will take place only under cold start conditions, if for example:
a. the transmission oil temperature is below a preprogrammed level of, e.g., 0xc2x0 Celsius and/or
b. the engine is idling at a higher speed than a preprogrammed value of, e.g., 1200 rpm, which would indicate that the idle speed is raised due to engine warm-up.
Preferably, the foregoing warm-up procedure is terminated and the clutch is taken out of engagement under the following conditions:
a. in the presence of activities to engage a start-up gear, e.g., by moving the drive mode lever from neutral to a drive mode, and/or
b. if the transmission oil temperature rises above a preprogrammed value of, e.g., 0xc2x0 Celsius, and/or
c. if the idling speed of the engine falls below a preprogrammed minimum value of, e.g., 900 rpm, which would indicate that the engine is warmed up or is about to stall, and/or
d. if the vehicle begins to move.
The re-engagement of the clutch according to the present invention can be inhibited by a suitable action of the driver, even if the foregoing conditions are otherwise met, for example by moving the brake pedal or the accelerator pedal out of their rest positions, or by any movement of the mode-selector or gear-shift selecting means.
The re-engagement of the clutch in accordance with the present invention is allowed to take place if the transmission is in neutral mode because the respective step for putting the vehicle in motion or for engaging a start-up gear has not been taken, or because the start-up gear has been automatically disengaged by intervention of the electronic control unit.